To facilitate an appreciation of the invention, this section may discuss the historical and technical background leading to the development of the invention, including observations, conclusions, and viewpoints that may be unique to an inventor. Accordingly, the background statements herein should not be construed as an admission regarding the content of the prior art.
A number of therapies have been developed to treat a variety of cancers. Many of these efforts have centered around chemotherapeutic regimens. In one particular combination chemotherapy regimen designed as a treatment for metastatic melanoma, response rates of 35-50% were reported with the “Dartmouth regimen” (a of combination DTIC, cisplatin, BCNU and tamoxifen), but the duration of survival has remained at 6 to 10 months. High rates of remission also have been reported for aggressive high-dose intensity chemotherapy1 and repletion of hematopoeisis with autologous bone marrow transplants. Nevertheless, the median duration of survival was short, approximately four months2.
Significant improvements in survival on the order of several years have been noted in a small percentage of melanoma patients undergoing certain immunotherapies. This includes active specific immunotherapy with cancer vaccines, as well as the use of nonspecific boosters of the immune system, such as interleukin-2 (IL-2) and interferon-alpha (IFN-α).3-5 
The identification of T-cell defined tumor antigens in melanoma has led to clinical trials that target cancer cells by attempting to augment the antigen-specific cellular immune response. This approach has been pursued in numerous vaccination strategies in which the antigens are delivered in an immunogenic context in an attempt to induce potent T cell responses in vivo. Although some clinical responses have been observed in the vaccine trials, the magnitude of the induced T-cell response has generally been low, or undetectable and correlated poorly with clinical responses. Immunization of melanoma patients with cancer antigens may increase the number of circulating CTL precursors; however it has not correlated with clinical tumor regression, suggesting a defect in function or activation in vivo.
Studies in mouse tumor models have demonstrated that adoptive immunotherapy, which involves in vitro immunization of T cells specific for one or more tumor antigens, may be efficacious with minimal toxicity. An obstacle in applying this strategy to the treatment of human tumors has been the identification of immunogenic antigens that render the tumor cells susceptible to CTL-mediated destruction. The isolation of tumor-reactive T cells from melanoma patients has led to the identification of some of the tumor antigens (epitopes) to which CTLs are directed. These include tyrosinase, MART-1/Melan A, gp100, and MAGE. Of these, tyrosinase and MART-1 are nearly universally expressed on melanoma and therefore represent a desired target choice for adoptive immunotherapy.6-13 
Adoptive T cell therapy involves the removal of T cells from the host environment where tolerogenic mechanisms are active in vivo in cancer patients and contributes to the ineffective responses demonstrated in this patient population. CD8+ T cells may be stimulated ex vivo to generate antigen-specific CTLs (see, e.g., U.S. Pat. No. 6,225,042). Early adoptive immunotherapy approaches used activated lymphocytes as a treatment for various cancers.14 Initially, lymphokine-activated killer cells (LAK), and later tumor-infiltrating lymphocytes (TIL), activated ex vivo with IL-2, were used, but the demonstration of efficacy was equivocal. These early, controlled clinical trials failed to show an advantage to the use of the ex vivo-activated cells over the direct administration of IL-2 to melanoma patients. More recent studies by Yee et al. (Fred Hutchinson Cancer Research Center)15 and Dudley et al. (NCI)16 have demonstrated the potential for certain adoptive T-cell therapeutic approaches. These studies involved use of either T-cell clones specific for MART-1 or gp100 and low-dose IL-2, or TILs expanded ex vivo with allogeneic feeder cells and high-dose IL-2. These studies confirmed that adoptive immunotherapy holds promise as a treatment of cancer, although its full development has been impeded by the lack of reproducible methods for ex vivo generation of therapeutic numbers of antigen-specific CD8+ CTLs.17 
Cytotolytic CD8+ T cells are a major line of defense against viral infections. CD8+ lymphocytes specifically recognize and lyse host cells that are infected with a virus. Although it would be desirable to harness the cytotoxic activity of CTLs, few in vitro/ex vivo procedures have been available to specifically activate CTLs. The identification of key melanoma-associated antigens and a method for specific in vitro activation of CTLs, allows for an efficient evaluation of adoptive immunotherapy for metastatic melanoma.15-18 
While it is possible to use naturally occurring antigen presenting cells (APCs) for CD8+ activation in vitro (e.g., dendritic cells, macrophages, autologous tumor cells), the efficiency of activation is low since the MHC Class I molecules of native APCs contain many other peptide epitopes, thus allowing minimal presentation of tumor-associated peptide epitopes. Most of these presented peptides represent normal, innocuous endogenous proteins. A more direct approach to this problem would be to activate CD8+ T cells specifically to those epitopes relevant to combating the disease, in this particular case, melanoma-associated antigens.
Recently, an artificial APC has been developed utilizing a Drosophila melanogaster (fruit fly) embryonic cell line, which expresses the major histocompatibility complex (MHC) Class I molecules.18,19 See also U.S. Pat. Nos. 6,225,042 and 6,355,479. Since the insect Drosophila lacks an advanced immune system, the TAP-1,2 peptide transporters, which are involved in the loading of peptide epitopes into the human Class I molecules, are absent. As a result, the transfected Class I molecules appear on the Drosophila cell surface as empty vessels. By incubating these transfected Drosophila cells with exogenous synthetic peptides that bind to the specific Class I molecules (i.e., tumor antigen T-cell peptide epitopes), all of the available Class I molecules may be occupied with MHC-restricted, specific peptide epitope(s). The high density expression of the Class I molecules presenting single or multiple epitopes, and the addition of key co-stimulatory molecules B7-1 (CD80), CD70, LFA-3 (CD58), and ICAM-1 (CD54) on these Drosophila APCs may permits the in vitro generation of potent, autologous cytotoxic CD8+ T cells, which are specific for the antigenic peptides.20 